<h2>DESCRIPTION</h2>

The <em>v.to.3d</em> module is used to transform 2D vector features
to 3D. Height (z-coordinate) of 3D vector features can be specified
by <b>height</b> parameter as fixed value or by <b>column</b>
parameter.

<p>
Flag <b>-r</b> enables to perform reverse transformation, i.e.,
transform 3D vector to 2D by omitting z-coordinate. Height of input 3D
features can be optionally stored in <b>column</b>.

<h2> NOTES</h2>

When transforming 2D vector features to 3D based on attribute, all
NULL values are silently converted to height 0.0.
<p>
Reverse transformation is possible for points and lines.
In case of lines, the reverse transformation should be used
only when all vertices of a line have the same z-coordinate
(for example contours).

<h2>EXAMPLES</h2>

<h3>Transform 2D vector features to 3D</h3>

<div class="code"><pre>
# convert z-values from string to double
v.db.addcolumn map=geodetic_pts columns="Z_VALUE_D double precision"
v.db.update map=geodetic_pts column=Z_VALUE_D qcolumn=Z_VALUE
v.db.select map=geodetic_pts columns=cat,Z_VALUE,Z_VALUE_D

# convert 2D vector point map to 3D based on attribute
v.to.3d input=geodetic_pts out=geodetic_pts_3d column=Z_VALUE_D
</pre></div>

<h3>Transform 3D vector features to 2D</h3>

<div class="code"><pre>
v.to.3d -rt input=elev_lid792_bepts output=elev_lid_2d
</pre></div>

<h2>SEE ALSO</h2>

<em>
<a href="v.transform.html">v.transform</a>,
<a href="v.extrude.html">v.extrude</a>,
<a href="v.drape.html">v.drape</a>
</em>

<h2>AUTHOR</h2>

Martin Landa, Czech Technical University in Prague, Czech Republic

<!--
<p>
<i>Last changed: $Date$</i>
-->
